It's party time for NATO — and not just because the alliance celebrates its 70th birthday in Washington this week.

U.S President Donald Trump, convinced of his success in pushing allies to spend more on defense, has stopped bludgeoning NATO and hinting that he wants to quit. Instead, he has almost — almost — become a cheerleader. The once-unlikely comity was on display Tuesday afternoon, when Trump met with NATO Secretary-General Jens Stoltenberg at the White House ahead of the alliance’s official gathering later this week.

Trump called it an “honor” to host Stoltenberg, saying the U.S. is with him “100 percent.”

“When I came it wasn’t so good, and now they’re catching up,” Trump said, referring to a push for NATO allies to increase defense spending. “Tremendous progress has been made.”

"The strength of NATO is that despite differences we have always been able to unite around our core task,"which is to protect and defend each other" — Senior NATO diplomat

It's not so long ago that things looked very different. Last July, Trump caused turmoil at a NATO summit in Brussels by unleashing a withering attack on Germany and threatening allies that the U.S. could "go our own way" unless they rapidly increase their military spending.

But Stoltenberg has proven to be a highly effective Trump-whisperer, repeatedly citing a figure of an extra $100 billion that NATO allies are in the process of spending on defense to help persuade the U.S. president that he is winning and the alliance is on the right track. For his efforts, Stoltenberg was rewarded last week with a two-year extension of his term, meaning he will stay in post until September 30, 2022.

NATO is also expanding. North Macedonia, having resolved its name dispute with Greece, is on track to become NATO's 30th member later this year. That adds a further dash of symbolism as NATO is already trumpeting its Four Thirties Readiness Initiative — the capability to deploy 30 combat ships, 30 land battalions and 30 air squadrons within 30 days.

The Four Thirties and the further expansion in the Balkans are designed to counter Russia, whose renewed military assertiveness since its invasion and annexation of Crimea in 2014 has propelled NATO to its greatest relevance since the end of the Cold War. Moscow's actions have cemented the view among most allies, particularly those in Eastern Europe, that collective defense, and the alliance that provides it, are essential.

Even Brexit, for all of the chaos that it has unleashed domestically, has only reinforced Britain's commitment to NATO, which will provide its most concrete bond to the Continent if and when it leaves the EU. And, after long delays, the alliance is now fully moved in to its gleaming new headquarters in Brussels.

"The strength of NATO is that despite differences we have always been able to unite around our core task," a senior NATO diplomat said this week, "which is to protect and defend each other."

Retired U.S. Air Force General Philip M. Breedlove, a former NATO supreme allied commander, said new dangers presented by Moscow far overshadow the recent strains in transatlantic relations.

"In the history of our alliance, we have lots of these perturbations, where we have had different members doing different things, we have had different factions," Breedlove told POLITICO in a recent interview in Brussels.

"But what we really haven't had in the past, to my mind, is a dedicated opponent that has all the tools and the willingness to subvert and attack in very sophisticated ways to drive us further apart ... now what we have is an opponent that knows how to in a very sophisticated organized, dedicated, heavy-presence way, that gets in there and exacerbates those cracks through hook and crook to drive us further apart."

Serious questions

Still, serious questions linger as NATO foreign ministers gather in the American capital to mark the 70th anniversary of the signing of the Washington Treaty — which launched the alliance — and Stoltenberg on Wednesday delivers a speech to Congress.

Military experts have expressed concern about NATO's preparedness to handle emerging rivals, how a traditional military alliance confronts asymmetrical threats — particularly terrorism but also hybrid and cyberattacks — and especially its failure so far to stop Russia's aggression, most recently on display in the Azov Sea.

Some allies have also lamented the Trump administration's decision to pull out of a nuclear treaty with Russia, even as they blame Moscow for violating the accord. NATO officials also concede that the focus on Russia, however necessary, has prevented the alliance from addressing other challenges, such as the rise of China.

U.S. Secretary of State Mike Pompeo, who will host his fellow NATO foreign ministers this week, pointedly refused to offer reassurance to the small Balkan nation or other allies when pushed on the issue earlier this year.

"The answer is coalitions can work when every member of the coalition is doing their fair share. That’s how these relationships have worked for an awfully long time. And unfortunately, some countries took a vacation for 20 years," he said.

More recently, during testimony last week before Congress, Pompeo said the 70th anniversary events would demonstrate steadfast U.S. dedication to NATO. He dismissed characterizations that Trump is a threat to the alliance and said the push to get allies to spend more would continue.

"This administration will once again reaffirm our commitment to our NATO allies and we will again ask them, because it is important, to do their share, to make sure that NATO is around for the next 70 years," Pompeo said.

Ivo Daalder, a former U.S. ambassador to NATO, said that in many visible ways, the alliance appears to be stronger, and U.S. commitment is notably greater.

"More American troops are deployed to Europe than they have been for many years," Daalder said. "Changes are being made in the force structure, the command structure." And he noted that Congress has stepped up to reassure allies. "Support on the Hill is stronger than it’s ever been, and public support is stronger," he said.

But Daalder noted that some doubts are impossible to erase. “There is a sense that the alliance is damaged, that American leadership is absent," he said. "People are worried. I’ve talked to plenty of people who are deeply concerned about questions they were not worried about before. Questions like if they are attacked, will the United States come to their aid?”

Those doubts help explain why NATO's heads of state and government are not gathering for the anniversary celebration in Washington but are expected to meet at another commemoration in London at the end of this year. When planning for the anniversary began in earnest last summer, leaders had just experienced the one-two punch of a disastrous G7 summit in Quebec and the tumultuous NATO summit in Brussels last July — all because of Trump's unpredictability.

Many allies credit Stoltenberg with ensuring that the State of the Union speech reflected a positive view of NATO.

Few had the stomach to risk a disastrous leaders' meeting in Washington and so plans shifted to organizing an event around a meeting of foreign affairs ministers, officials and diplomats said. (NATO's official explanation is that two leaders' summits are never held within less than a year and that the London meeting in December would allow for a broader agenda.)

Since last year's turmoil, officials in Brussels and Washington said, there has been a marked improvement in Trump's attitude toward NATO — a change reflected in his State of the Union address in February.

"We are also getting other nations to pay their fair share," Trump declared. "For years, the United States was being treated very unfairly by NATO — but now we have secured a $100 billion increase in defense spending from NATO allies."

Many allies credited Stoltenberg with ensuring Trump expressed a positive view of NATO. On a visit to Washington just before the speech, Stoltenberg used an interview on Fox News, Trump's preferred channel, to highlight the increased spending by allies, with a special focus on the $100 billion figure that the president cited in his speech.

Even Trump's unconventional assertion last month that he was considering NATO membership for Brazil was generally considered relatively positive for the alliance given that he floated the idea as a compliment during a visit from Brazilian President Jair Bolsonaro.

Tensions between Trump and individual allies have generally eased — with the notable exception of Germany. Trump and his administration continue to hammer the country not just over military spending but also in terms of trade ties.

“Overall, the sense is that NATO has improved with one possible exception: that sentiment toward Germany has worsened because you’re seeing more stories that they’re not even going to meet the increase they were talking about," said one Senate aide. "So I can see a narrative emerging that Trump refers to Germans as a bunch of deadbeats.”

Ahead of this week's meeting in Washington, Germany has developed a sharper response to Trump's criticism, with officials stressing that Berlin intends to fully meet its NATO "capability" goals by 2024, even though annual military spending will increase only to 1.5 percent of GDP — well short of NATO's target of 2 percent. Many analysts believe it would be unwise for Germany to move too quickly toward 2 percent given the large size of its economy, and there are questions about whether the increased spending would be used effectively or just to hit the numerical goal.

NATO foreign ministers attend a working dinner at the Parc Cinquantenaire during a NATO summit in Brussels | Yves Herman/AFP via Getty Images

Officials also note that of the $100 billion in increased spending through 2020 — the number Stoltenberg and Trump trumpet in public remarks — roughly $30 billion comes from Germany.

Asked about Germany's commitment at a news conference on Monday in Brussels, Stoltenberg practised his well-honed tightrope-walking skills. "I expect Germany to make good on the pledge Germany made together with all other NATO allies," he said. "And that’s partly about spending but also about capabilities."

He also noted Germany's substantial contributions to NATO missions in Afghanistan and in the Baltics.

At the news conference, Stoltenberg knocked down a question about a report written by two former U.S. ambassadors to NATO, Douglas Lute and Nicholas Burns, citing Trump’s lack of leadership as a risk to NATO.

"What I am absolutely convinced about is that what we see now is a strong commitment by the United States to NATO, and I say that partly because that is what has been stated by the president," Stoltenberg said.

However, some experts say internal tensions within the alliance have distracted somewhat from NATO's bigger challenges, including how to deal with the collapse of the Intermediate-Range Nuclear Forces Treaty with Russia, which provided an umbrella of security for European allies, and also how to cope with new concerns about China.

"Here in the alliance we don’t have a consolidated position on China right now," a senior NATO diplomat said. "What we are having right now is a sort of orientation debate. So far, China was not on our radar. It is now. I think we need to have a solid, serious, analytical discussion about what China means for Europe and its security."